Hammer construction



Oct. 18, 1966 c. J. HELMS HAMMER CONSTRUCTION 2 Sheets-Sheet 1 Filed Aug. 2, 1965 //v l/EA/TO/Q CZ/n oreo 6 54 44 571W M QJM AM A FOR/V1575 C. J. HELMS Oct. 18, 1966 HAMMER CONSTRUCTION 2 Sheets-Sheet 2 Filed Aug. 2, 1965 C1 #1000 J. /1LMS law/J my (Ia/M lwM A 7TO/QNEY5 United States Patent Ofiice 3,279,364 Patented Oct. 18, 1966 3,279,364 HAMMER CONSTRUCTION Clifiord J. Helms, Woodland Hills, Calif., asslgnor to Data Products Corporation, Culver City, Calif., a corporation of Delaware Filed Aug. 2, 1965, Ser. No. 476,294 12 Claims. (Cl. 101-43) This invention relates generally to high speed printing apparatus and more particularly to improved impact devices for use therein.

US. Patent 3,172,352 discloses a printing hammer, including, in a preferred embodiment, a pair of flat springs which conduct current to a coil mounted on a hammer shank. The coil is situated within a magnetic field provided by spaced permanent magnets. It is pointed out in the cited patent that such a construction provides a low friction hammer which can "be rapidly propelled, as a consequence of the interaction between the current in the coil and the magnetic field, from a rest position to an impact position, i.e., into engagement with a printing drum. (It will be understood throughout that the hammer does not actually engage the printing drum inasmuch as the paper being printed upon and an inked ribbon is at all times disposed between the hammer and the drum.) Inasmuch as it is desirable that the drum rotate continually if high printing speeds are to be achieved, it is important that the travel time of the hammer be minimized if the printed characters are to be aligned. That is, a signal to start the hammer traveling toward the drum must be provided prior to the character on the drum to be printed moving into printing position. If the travel time interval is relatively long, then a small variation in drum speed during this interval will result in the character being struck either prior or subsequent to it reaching its proper printing position. Thus, by reducing the hammers travel time, greater character alignment and a generally improved printing quality can be achieved. In addition to travel time being significant, printing quality is also affected by contact time, i.e., the interval that the shank is actually in contact with the paper and urging it against the drum. If the contact time is excessive, the printed characters will be smeared since the drum is continually rotating. In order to achieve a maximum printing speed, it is also essential that the recovery time of the hammer 'be minimized so that no time need be wasted between successive actuations of a hammer.

The desire to minimize travel, contact, and recovery time, assuming that other conditions such as the spring constant of the paper, the force applied to the hammer, etc. are fixed, suggests that the mass of the hammer be minimized. US. patent application Serial No. 463,263, filed on June 11, 1965, entitled, Printing Hammer, by Clifford J. Helms, and assigned to the same assignee as the present application, discloses a hammer construction which permits travel, contact, and recovery times to be minimized. More particularly, the cited patent application discloses a hammer construction comprised of a rigid housing having a coil therein and carrying an impact tip thereon which housing is supported on a pair of flexible conductive members for substantially rotational movement between a rest position and an impact position. It is pointed out in the cited patent application that by selecting a geometry for the hammer construction such that the forces applied to the impact tip act at the center of percussion with respect to the point about which the housing is rotated, the reaction on the supporting members is substantially reduced to zero and the effective mass of the hammer acting at the impact tip is minimized.

The present invention is directed to a hammer construction having characteristics which make it less expensive and more reliable than previously known hammer constructions. In addition, a hammer constructed in accordance with the present invention can be more ofiiciently operated than previously known hammers.

Briefly, in accordance with a first aspect of the present invention, acoil structure comprised of a flat rigid single turn coil structure or a plurality of such coil structures laminated together, is utilized in lieu of multiturn coiled conductors supported within a rigid housing. A single turn or laminated coil structure can be provided at a lower cost than previously known coil structures inasmuch as the single turn coil structure can be inexpensively formed from aluminum or copper material. It should be appreciated that such a coil structure is also inherently more reliable than prior art coil structures.

Utilization of a single turn coil structure or a few such structures laminated together of course requires that a greater magnitude coil current be used than in previous multiturn coil structures if the same propelling force as was previously available is to be developed, assuming of course the existence of similar permanent magnet fields, etc. In accordance with one aspect of the present invention, high coil currents are developed by connecting the coil terminals across a transformer secondary winding. The power loss in the current carrying supporting springs, in p the previously mentioned hammer embodiments, represents wasted power which is of course proportional to the square of the current through the springs. Thus, the elficiency of a high current carrying single turn or laminated coil structure could be disturbingly low, due to the power loss in the supporting springs.

Accordingly, in accordance with a further aspect of the present invention in order to avoid wasting power in this manner, current is induced in the movably mounted coil structure via transformer action. That is, a transformer core is inductively coupled to the coil structure which itself functions as a transformer secondary winding. A multiturn primary winding is also coupled to the transformer core. By driving a current through the primary winding, a current will be induced in the coil which will of course interact with the permanent magnetic field to thereby exercise a propelling force on the coil structure.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself both as to its 0rganization and method of operation, as well as additional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanying drawings, in which:

FIGURE 1 is a side sectional view of one embodiment of a printing hammer constructed in accordance with the present invention;

FIGURE 2 is a vertical sectional view taken substantially along the plane 22 of FIGURE 1 and illustrating a front view of the hammer of FIGURE 1;

FIGURE 3 is a perspective view of a laminated coil structure which can be alternatively employed in .the embodiment of FIGURE 1;

- FIGURE 4 is a perspective view of a further embodiment of the invention; and

FIGURE 5 is a rear view of a portion of a hammer bank comprised of hammers as shown in FIGURE 4.

Attention is now called to FIGURES l and 2 of the drawings which illustrate a high speed line printing apparatus which employs one form of printing hammer constructed in accordance with the present invention. More particularly, the printing apparatus includes a printing drum 10 which is adapted to continually rotate about an axis through the center thereof. Raised characters (not shown) are formed on the circumferential surface of the drum 10. The characters are arranged in tracks, each track corresponding to a different position on a line to be printed. Thus, if a maximum of 132 characters is to be printed across any one line, the printing drum will preferably have 132 tracks, with each track containing all of the characters that the apparatus is adapted to print.

A bank of printing hammers 12 is provided spaced from the drum 10. The hammer bank 12 usually includes a number of hammers equal to the number of tracks formed on the drum 10. Positioned between the hammer bank 12 and the drum 10 is a printing ribbon 14 and the paper 16 to be printed upon. In the operation of the printing apparatus, the paper 16 is incrementally driven (by means not shown) to each new line position. After the paper settles into a new line position, a signal is usually provided to control means (not shown) which functions to actuate each hammer just prior to the character it is to print moves into printing position. When the hammer is actuated, it moves from its rest position toward the drum 10 and strikes the paper 16 urging it against the ribbon 14 and against the appropriate character on the drum, thereby printing it on the paper 16. As previously noted, in order to assure good quality printing, both the travel and contact time of the hammers should be minimized as much as possible.-

In accordance with the present invention, a printing hammer 18 is provided including a rigid flat unitary single turn coil structure 20 formed of conductive material such as aluminum or copper. A gap 22 is formed in the coil structure thereby defining coil terminals on either side thereof. The gap 22 can be filled with an insulative material (not shown). The coil structure 20 can be formed from any one of several known techniques such as stamping, precision, casting, etc. An impact tip 28, which can also be formed of aluminum or copper, is carried on the upper end of the coil structure 20 and preferably in electrical contact therewith.

The coil structure 20 is supported on a pair of electrically conductive support members and 32 which preferably comprise flat spring members having enlarged first ends 34 and 36 which are secured to opposite sides of the coil structure 20 and enlarged second ends 38 and 40 which are structurally and electrically secured to conductive portions 41 and 42 of a supporting block 43. The conductive portions 41 and 42 are insulated from one another by epoxy 44 or such. As can clearly be seen in FIGURE 1, the supporting members 30 and 32 extend in planes which intersect each other at point 45. Portions of the coil structure 20 preferably extend below the point 45 in order to lower the center of rotation of the coil structure as described in the aforecited patent application.

A support assembly 46 is provided which carries a plurality of individually adjustable backstops 48 adapted to engage the rear end 50 of the impact tip 28 when the printing hammer is in its rest position. The front end 52 of the impact tip 28 is of course adapted to force the paper 16 against the ribbon 14 and drum 10.

The first ends 34 and 36 of the conductive support members 30 and 32 are electrically secured to the coil member 20 on opposite sides of the gap 22 by some conductive material such as solder. The second ends 38 and 40 of the support members 30 and 32 are respectively electrically and structurally secured to conductive portions 41 and 42 of the supporting block 43. The rear edges of the portions 41 and 42 are preferably rounded so that they can be received in V-grooves formed in surface 74 of a positioning block 78. Set screws 7? can be used to secure the supporting block 43 to the positioning block 78. The utilization of precision-formed V-grooves in surface '74 permits easy registration of all of the hammers 18. When in position, all of the impact tips 28 should be in substantial alignment with the center line of the drum 10.

The conductive portions 41, 42 of the supporting block 43 are electrically connected across a secondary winding (not shown) on a transformer core 80. The conductive portions 41 and 42 are preferably formed of a heavy gauge copper or other highly conductive material in order to minimize power loss therein. The ends of the supporting members 30 and 32 are enlarged of course to reduce resistance and power loss in the current path. In order to efiiciently provide a substantial current through the coil structure, the transformer core will probably require a large cross-section which may in turn require that the transformer cores be arranged in two tiers spaced either vertically or horizontally from one another.

The hammer bank 12 can consist of two sections, the first section comprises of hammers 18 which are supported above a lower positioning block 78 and a second section comprised of hammers 18' depending from an upper positioning block (not shown). Similarly, lower and upper permanent magnet sections 96, 36 are provided each defining a plurality of gaps, each gap adapted to receive one of the hammers 18, 18 therein. The permanent magnets can be arranged substantially as illustrated in US. patent application Serial No. 419,509, filed December 18, 1964, and assigned to the same assignee as the present application. However, Whereas the permanent magnet banks are illustrated as being two deep in that patent application inasmuch as the coil projecting from each shank extends above and below the shank so that each hammer utilizes magnets both above and below its shank, in accordance with the present invention the permanent magnet bank need only be one deep since half of the hammers will utilize the lower magnet bank 96 and half of the hammers will utilize the upper bank 96. The magnet banks can be cantilevered from the support assembly 46 as illustrated.

In the operation of the printing hammer 18 illustrated in FIGURES 1 and 2, in order to propel the impact tip 28 against the drum 10, an electrical current is produced by the transformer secondary winding (not shown) and supplied to the conductive portions 41, 42. Consequently, a current will flow through the coil structure 20 and support members 30 and 32 thus resulting in the generation of a first magnetic field which interacts with a second magnetic field produced by the parmanent magnets on either side of the coil structure 20. The interaction will result in a force being applied to the coil structure 20 which is perpendicular both to the permanent magnet field and the direction of current within the coil structure 20. Inasmuch as the current fiow through the coil structure 20 is substantially in a vertical direction within the plane of the paper shown in FIGURE 1, and the magnetic field is perpendicular to the plane of the paper, the resulting force on the coil structure 20 will be horizontally directed within the plane of the paper therefore acting to propel the impact tip 26 against the drum 10.

As demonstrated in the aforecited US. patent application Serial No. 463,263, the coil structure carried by the support members 30 and 32 will exhibit substantially rotational movement about the point 45 defined by the intersection of the support members when in a rest position. As is also pointed out in that patent application, if the geometry of the hammer is selected so that the impact tip 28 is positioned substantially at the center of percussion with respect to the center of rotation 45, the reactive forces acting on the support members will be minimized and in addition the effective mass of the hammer will also be minimized thus minimizing both travel and contact times.

From the foregoing description of FIGURES 1 and 2, it should be appreciated that an improved hammer construction has been disclosed herein in which both the structural and electrical properties of a rigid unitary single turn coil preferably formed of aluminum or copper has been employed. That is, the structural properties of the coil structure have been employed to carry the impact tip 28 while the electrical properties thereof have been employed to conduct current between the ends thereof for interaction with the permanent magnetic field in order to develop a propelling force. As previously pointed out, a flat rigid unitary coil member as shown in FIGURE 1 which can be formed by fabrication methods such as stamping, casting, etc., can be provided at a lower cost than a multiturn coil conductor carried within a housing. In previous hammer embodiments wherein a coiled multiturn conductor is carried within a housing, the electrical characteristics of the coil are utilized while the structural characteristics of the housing are utilized. Herein, both the structural and electrical characteristics of a unitary element are both employed. In addition to being less costly, a coil structure as disclosed herein has greater inherent reliability than a coiled conductor supported within a housing. That is, there is considerably less likelihood that the current path in the unitary coil structure'illustrated herein will be ruptured than in prior art coil structures.

Since the propelling force applied to the hammer is proportional to the magnitude of the permanent magnetic field, the magnitude of the current through the coil, and the number of coil turns within the magnetic field, it should be clear that if the number of turns is reduced by a factor of 100 for example, the current must be increased by that same factor if the same force is to be developed, assuming that the magnitude of the magnetic field remains constant. Inasmuch as the cross-section of the unitary single turn coil structure can be many times that of a single turn of the coiled conductive ribbon previously disposed within a housing, a current can be developed by the transformer and driven through the coil structure whose magnitude is many times greater than the magnitude of current previously driven through the coiled conductor. However, in order to develop even greater propelling forces, -a pluraliy of unitary coil members can be laminated together to form a rigid structure as shown in FIGURE 3 wherein three unitary coil members 110, 112, and 114 are held together by an insulating epoxy material (not shown) provided therebetween. The conductive support members 30, 32 will be respectively connected to the first end of coil member 110 and the second end of coil member 114. Jumpers 116 and 118 will respectively connect the second ends of coil member 110 to the first end of coil member 112 and the second end of coil member 112 to the first end of coil member 114.

Although a unitary coil member as shown in FIG- URES 1 and 2 or a laminated coil structure as shown in FIGURE 3 provides enough cross-sectional area to carry sufiicient current for all contemplated applications of the hammer 18, as the magnitude of the current is increased, the power loss, and thus the efiiciency, decreases as a consequence of the power loss in the conductive spring members 30 and 32. More particularly, inasmuch as power loss is proportional to the square of the current, the tremendous increase in current required as a consequence of reducing the number of turns by a hundred fold, causes a tremendous increase in power -loss through the spring members. Although the resistance of the spring members can be minimized by providing them with the enlarged ends illustrated to thus increase their cross-sectional area, a limit in resistance reduction is rapidly reached since as the springs get =larger, they tend to lose their necessary compliance and fiexural characteristics. Consequently, in accordance with a further aspect of the present invention as is illustrated in FIG- URES 4 and 5, current is directly induced, via transformer action, into the rigid flat unitary coil member 120. The coil member 120 is similar to that illustrated in FIGURES 1 and 2 except however it defines a closed conductive loop instead of including the gap 22 (FIG- URE 1). The unitary coil member 120 can also be formed by any one of a plurality of known fabrication techniques. A transformer core 122 is threaded through the central opening 124 of the unitary coil member 120.

A multiturn primary winding 126 is wound on the transformer core 122.

The unitary coil member is supported on a pair of spring members 128 and 130. More particularly, first ends of the spring members 128 and 130 are secured to opposite sides of the unitary coil member 120. Second ends of the spring members 128 and 130 are structurally secured to a support block 132 which is registered within a positioning block 134 provided with positioning V-grooves 135. In the operation of the embodiment of FIGURE 4, in order to apply a propelling force to the unitary coil member 120, a current is driven through the primary winding 126 on the transformer core 122. As as consequence, a current is induced in the unitary coil member 120 which acts as a transformer secondary winding. This current of course interacts with the magnetic field produced by the permanent magnets disposed on either side of the coil member 120 to thereby cause a horizontally directed force within the plane of the paper to be applied to the coil member. Consequently, the coil member 120 will substantial-1y rotate about a point 136 defined by the intersection of the support members 128 and 130 in their rest position.

Preferably, the impact tip 138 carried by the unitary coil member 120 should be positioned at the center of percussion with respect to the center of rotation 136. With this geometry, the hammer will have its lowest effective mass and therefore travel and contact times will be minimized. In addition, the reactive forces on the support members 128 and 130 will be minimized. Because of this, and also because the support members 128 and 130 are no longer called upon to conduct current, they can comprise very simple and inexpensive spring members. The positions of the transformer cores 122 can be staggered as shown in FIGURE 5 in order to enable terial which is'well suited for a transformer core for the indicated application is Supermendur.

From the foregoing, it should be appreciated that an improved hammer construction has been shown herein wherein a less expensive and improved hammer has been provided utilizing a flat rigid unitary coil structure which avoids the necessity of providing a coiled conductor and a housing therefor. Substantial currents can be driven through the coil structure via transformer action and in one embodiment of the invention the coil structure itself is made to comprise the transformer secondary, thereby considerably reducing the requirements made of the supporting spring members. Although not specifically illustrated, it should be appreciated that transformer action can be utilized to induce a current in a laminated coil structure of the type shown in FIGURE 3 and also in prior art coil structures comprised of multiturn coiled con ductors disposed within coil housings either through supporting members as shown in FIGURES l and 2 or directly as shown in FIGURES 4 and 5. Further, although the provision of a unitary coil member or laminated coil structure has been shown only in conjunction with rotatable mounting means, it should be apparent that such coil structures can be utilized in hammers in which the structure is propelled linearly as for example as described in the aforecited U.S. Patent No. 3,172,352. Similarly, currents can be induced in coil structures mounted for linear movement by transformer action.

Accordingly, inasmuch as it is clearly recognized that other structural configurations can be provided which depend on the inventive concepts disclosed herein and which do not depart from the true scope and spirit of the invention, it is intended that such modifications fall within the scope of the invention as claimed.

What is claimed is:

1. A hammer construction comprising:

means for establishing a first magnetic field;

a flat rigid unitary coil structure;

means supporting said structure in said first magnetic field for movement between a rest position and an impact position; and

means for driving current through said coil structure for interacting with said first magnetic field to apply a force to said structure to move it from said rest position to said impact position.

2. The hammer construction of claim 1 wherein said coil structure has first and second terminals;

said means supporting said structure including first and second conductive springs respectively connected to said first and second terminals; and

means coupling said means for driving current to said first and second conductive springs.

3. The hammer construction of claim 1 wherein said means for driving current includes a transformer core; and

means inductively coupling said transformer core to said coil structure.

4. A hammer construction comprising:

means for establishing a first magnetic field;

a rigid coil structure comprised of one or more fiat single turn unitary conductive coil members connected in series;

means supporting said structure in said first magnetic field for movement between a rest position and an impact position; and

means for driving current through said coil members for interacting with said first magnetic field to apply a force to said structure to move it from said rest position to said impact position.

5. A hammer construction comprising:

means for establishing a first magnetic field;

a rigid structure including a current conducting means;

means supporting said structure in said first magnetic field for movement between a rest position and an impact position;

means for driving current through said current conducting means for interacting with said first magnetic field to apply a force to said structure to move it I from said rest position to said impact position; said means for driving current including a transformer core; and means inductively coupling said transformer core to said current conducting means.

6. A printing hammer comprising:

a rigid coil structure comprised of at least one fiat unitary conductive member energizable to generate a first magnetic field;

means supporting said rigid structure for substantially rotational movement about a first axis; and

means establishing a second magnetic field adapted to interact with said first magnetic field.

7. The hammer construction of claim 6 including:

an impact tip; and

means mounting said impacttip on said coil structure.

8. The hammer of claim 7 wherein said impact tip is positioned substantially coincident with the center of permeans inductively coupling said transformer core to said conductive member for energizing it to generate said first magnetic field. 12. A printing hammer comprising: a rigid coil structure including a current conducting means energizable to generate a first magnetic field; means supporting said rigid structure for substantially rotational movement about a first axis; means establishing a second magnetic field adapted to interact with said first magnetic field; and

means for energizing said current conducting means including a transformer core and means inductively coupling said transformer core to said current conducting means.

References Cited by the Examiner UNITED STATES PATENTS 3,172,353 3/1965 Helms 101-93 ROBERT E. PULFREY, Primary Examiner.

DAVID KLEIN, Examiner.

W. F. MCCARTHY, Assistant Examiner.

l/1963 Goin 101-93 

1. A HAMMER CONSTRUCTION COMPRISING: MEANS FOR ESTABLISHING A FIRST MAGNETIC FIELD; A FLAT RIGID UNITARY COIL STRUCTURE; MEANS SUPPORTING SAID STRUCTURE IN SAID FIRST MAGNETIC FIELD FOR MOVEMENT BETWEEN A REST POSITION AND AN IMPACT POSITION; AND MEANS FOR DRIVING CURRENT THROUGH SAID COIL STRUCTURE FOR INTERACTING WITH SAID FIRST MAGNETIC FIELD TO APPLY A FORCE TO SAID STRUCTURE TO MOVE IT FROM SAID REST POSITION TO SAID IMPACT POSITION. 